Red Shirts a Wild Card in Thailand's Political Drama

ROI ET, Thailand—While Thailand braces for contentious elections that could spark more violence in the capital, broader ideological battles are playing out here in the country's hinterlands.

A few days ago, a mysterious banner appeared on an overpass in Phayao in northern Thailand, warning that the north of the country could break away from Bangkok and the south. "There is no justice. I want to split the country," it read, apparently referring to how protesters in Bangkok are trying to topple Prime Minister...